1. Field of the Invention
The invention relates generally to the field of power systems, and, more particularly, to a Quasi-Isothermal Brayton Cycle power system.
2. Description of the Related Art
For mobile applications, such as an automobile or truck, generally it is desirable to use a heat engine that has the following characteristics:
Internal combustion to reduce the need for heat exchangers;
Complete expansion for improved efficiency;
Isothermal compression and expansion;
High power density;
High-temperature expansion for high efficiency;
Ability to efficiently xe2x80x9cthrottlexe2x80x9d the engine for part-load conditions;
High turn-down ratio (i.e., the ability to operate at widely ranging speeds and torques;
Low pollution;
Uses standard components with which the automotive industry is familiar;
Multifuel capability; and
Regenerative braking.
There are currently several types of heat engines, each with its own characteristics and cycles. These heat engines include the Otto Cycle engine, the Diesel Cycle engine, the Rankine Cycle engine, the Stirling Cycle engine, the Erickson Cycle engine, the Carnot Cycle engine, and the Brayton Cycle engine. A brief description of each engine is provided below.
The Otto Cycle engine is an inexpensive, internal combustion, low-compression engine with a fairly low efficiency. This engine is widely used to power automobiles.
The Diesel Cycle engine is a moderately expensive, internal combustion, high-compression engine with a high efficiency that is widely used to power trucks and trains.
The Rankine Cycle engine is an external combustion engine that is generally used in electric power plants. Water is the most common working fluid.
The Erickson Cycle engine uses isothermal compression and expansion with constant-pressure heat transfer. It may be implemented as either an external or internal combustion cycle. In practice, a perfect Erickson cycle is difficult to achieve because isothermal expansion and compression are not readily attained in large, industrial equipment.
The Carnot Cycle engine uses isothermal compression and adiabatic compression and expansion. The Carnot Cycle may be implemented as either an external or internal combustion cycle. It features low power density, mechanical complexity, and difficult-to-achieve constant-temperature compressor and expander.
The Stirling Cycle engine uses isothermal compression and expansion with constant-volume heat transfer. It is almost always implemented as an external combustion cycle. It has a higher power density than the Carnot cycle, but it is difficult to perform the heat exchange, and it is difficult to achieve constant-temperature compression and expansion.
The Stirling, Erickson, and Carnot cycles are as efficient as nature allows because heat is delivered at a uniformly high temperature, Thot, during the isothermal expansion, and rejected at a uniformly low temperature, Tcold, during the isothermal compression. The maximum efficiency, xcex7max, of these three cycles is:       η    max    =      1    -                  T        cold                    T        hot            
This efficiency is attainable only if the engine is xe2x80x9creversible,xe2x80x9d meaning that the engine is frictionless, and that there are no temperature or pressure gradients. In practice, real engines have xe2x80x9cirreversibilities,xe2x80x9d or losses, associated with friction and temperature/pressure gradients.
The Brayton Cycle engine is an internal combustion engine that is generally implemented with turbines, and is generally used to power planes and some electric power plants. The Brayton cycle features very high power density, normally does not use a heat exchanger, and has a lower efficiency than the other cycles. When a regenerator is added to the Brayton cycle, however, the cycle efficiency is increased. Traditionally, the Brayton cycle is implemented using axial-flow, multi-stage compressors and expanders. These devices are generally suitable for aviation in which aircraft operate at fairly constant speeds; they are generally not suitable for most transportation applications, such as automobiles, buses, trucks, and trains, that must operate over widely varying speeds.
The Otto cycle, the Diesel cycle, the Brayton cycle, and the Rankine cycle all have efficiencies less than the maximum because they do not use isothermal compression and expansion steps. Further, the Otto and Diesel cycle engines lose efficiency because they do not completely expand high-pressure gasses, and simply throttle the waste gasses to the atmosphere.
Therefore, a need has arisen for a device that meets the above-mentioned and other characteristics for both mobile and stationary engines.
A need has also arisen for a device that overcomes these and other deficiencies.
An engine is disclosed. According to one embodiment of the present invention, the engine comprises a compressor, and combustor, and an expander. The compressor compresses ambient air. The combustor bums the compressed air, and produces exhaust gasses. The expander receives the exhaust gases from the combustor, and expands the exhaust gasses. The compressor may be a gerotor compressor or a piston compressor having variable-dead-volume control. The expander may be a gerotor expander or a piston expander having variable-dead-volume control.
In another embodiment, an engine comprises a piston compressor, a combustor, a piston expander, and a pressure tank. The piston compressor compresses ambient air. The combustor bums the compressed air, and produces exhaust gasses. The piston expander receives the exhaust gasses from the combustor, and expands the exhaust gasses. The pressure tank receives and stores the compressed air from the compressor.
In another embodiment, a gerotor compressor comprises an inner gerotor, and an outer gerotor. The inner gerotor and the outer gerotor are driven so that they do not touch. The gerotors may be cantilevered or non-cantilevered.
In another embodiment, a gerotor expander comprises an inner gerotor, and an outer gerotor. The inner gerotor and the outer gerotor are driven so that they do not touch. The gerotors may be cantilevered or non-cantilevered.
The engine of the present invention has many potential mobile power applications, including use in locomotives, the marine industry, tractor/trailers, busses, and automobiles. The engine of the present invention also has many potential stationary power applications, including, inter alia, electricity generator, and motive power for industrial equipment.
A technical advantage of the present invention is that the compressor and expander have rotary motion, which avoids the cost, complexity, weight, and size associated with transforming the linear motion of conventional pistons/cylinders into rotary motion.
Another technical advantage of the present invention is that the compressor and expander have a high xe2x80x9cturn-down ratioxe2x80x9d meaning they can operate efficiently at both high and low speeds.
Yet another technical advantage of the present invention is that the compressor and the expander are positive displacement devices that allows them to operate at low speeds in low-power applications.
Another technical advantage of the present invention is that the gerotor compressor and expander are perfectly balanced which virtually eliminates vibrations.
Another technical advantage of the present invention is that the engine is very responsive and accelerates quickly, much like a Wankel engine, because of its small size and light weight.
Another technical advantage of the present invention is that the gerotor compressor is robust, allowing liquid water to be sprayed for cooling during compression.
Another technical advantage of the present invention is that, in mobile applications, the expander can be independently decoupled from the drive train, allowing regenerative braking by operating the compressor from the kinetic energy in the vehicle.
Yet another technical advantage of the present invention is that, in mobile applications, the compressor can be independently decoupled from the drive train, allowing the expander to put all of its power into accelerating the vehicle giving the vehicle a power boost during startup.
Another technical advantage of the present invention is that there is little pollution emitted because of the high efficiency of the tubular combustor.
Another technical advantage of the present invention is that the tubular combustor can bum almost any fuel.
Another technical advantage of the present invention is that an electric starter motor is not needed because stored compressed air can be used to start the engine.
Another technical advantage of the present invention is that the engine is quiet because gases exit the expander at about 1 atm. No muffler should be needed.
Another technical advantage of the present invention is that engine lubricant, such as oil, should last a long time because there is no blow-by of incompletely combusted products.
Another technical advantage of the present invention is that there are very few moving parts, which should allow the engine to be very reliable with a long life.
Another technical advantage of the present invention is that the engine is extremely efficient; it approximates the Ericsson cycle, a reversible engine that is Carnot efficient.